Process of making negatives in metal of metal objects of substantially smooth surface



Patented Sept. 5, 1939 PATENT OFFICE PROCESS OF MAKING NEGATIVES 1N METAL OF METAL OBJECTS OF SUBSTANTIALLY SMOOTH SURFACE William C. Reid, Chicago, Ill., asslgnor to Metallizing Engineering Company, Inc., New York, N. Y., a corporation of New Jersey No Drawing. Application September 7, 1937,

Serial No. 162,831

2 Claims. (Cl. 22-200) This invention relates to a new and useful process of making negatives in metal of metal objects of substantially smooth surface.

It is old to apply a coating of metal to objects of metal by the use of a metal spray gun, i. e., a device by which metal particles are directed against the surface of the object by a blast of air or other gas. In a type of spray gun commonly used for this purpose a rod or wire of solid metal is fed progressively into a melting zone and as rapidly as it melts is propelled against the surface to be sprayed by a suitably directed blast of air or other gas. Another form of gun which may be so employed feeds particles of powdered metals to the heating zone and these are propelled upon the surface by a suitably directed blast of air or other gas. In still another form of gun which may be employed molten metal is sprayed and is subdivided and propelled against the surface by a suitably directed blast of air or other gas.

Generally speaking; unless the surface of the metal base against which the spray is directed is relatively rough or porous, the sprayed metal will not adhere and accumulate on the base and no coherent coating will build up. For this reason in the commercial application of the spraying process, unless the metal base to be sprayed has a substantially rough or porous surface, the surface must be roughened or rendered porous by suitable means such as sand blasting, grit blasting, ma-

chlning, acid etching or the like.

If the coating could be so applied to a rough or porous surface so as to be removable, the removed surface would carry the irregular and roughened surface of the base to which it was applied and it is for this reason impossible starting with such abase to make negatives characterized by a smooth surfaceand accuracy and detail of impressions. I

It is desirable to make accurate negatives or molds and reproductions or replicas in metal of metal objects of substantially smooth surface and by the force of the blast from the spray gun or if a it forms flakes upon the metal base these flakes curl and show the absence of any firm attachment to the metal base.

At the temperature of incipient adhesion and within the temperature range somewhat above the temperature of incipient adhesion the sprayed metal will accumulate upon the metal surface to which it is applied and form a coherent coating thereon. This coating is, however, detachable and may be removed intact by thermo or mechanical means for example it may detach itself on cooling or if the base to which it is applied is of a character which will not be injured or destroyed by quenching, the applied coating may be loosened by rapid cooling as for example by quenching and the applied coating thereafter removed. The upper limit of the permissible temperature range is the temperature at which inseparable adhesion between the base and applied metal occurs and at which the applied coating .cannot be removed intact by thermo or mechanical means. Between the temperature of incipient adhesion and the temperature of inseparable adhesion any intermediate degree of adhesion may be obtained by appropriate regulation of the temperature. The metal base must be at the desired temperature until a coherent coating has been formed although as soon as the surface has become entirely coated by the sprayed metal the deposition of the metal may be continued until a desired thickness has been obtained without regard to the temperature of the metal base while continuing the spraying.

In the practical application of my process the metal base to be covered is pro-heated to a point 40 below this range but if the surface is extensive itis advisable to maintain the temperature by heat- 4 ing the piece in some manner during the spraying operation.

The temperature of incipient adhesion and the temperature of inseparable adhesion are dependent upon the composition of the sprayed metal,

the composition of the metal base and upon the degree of-smoothness of the surface of the meta? base. These temperatures may, howeverf'f-o practical purposes be determined in the'following manner. Test specimens of the base-metal are placed in a suitable furnace in which the temperature is accurately measured and in which the temperature is' gradually rising. Test-specimens are taken from the furnace at intervals and may conveniently be'taken whenever the temperature has risen an increment of 25 F. When a test specimen is taken the spraygun is passed immediately over the specimen spraying onto the specimen the metal to be applied by spraying. As the temperature of the furnace rises, a point will be reached at which the sprayed metal shows a definite adhesion to the test specimens and the formation of a coherent coating thereon. Each test piece ,should be sprayed immediately on removal from the furnace so that no appreciable drop in temperature has occurred before the spraying operation'and the specimen is substantially at the indicated furnace temperature. The temperatureof the test piece at which the sprayed metal first shows definite adhesion and formation of coherent coating, may for practical purposes be taken as the temperature of K incipient adhesion and the process may be carried out at this temperature. The temperature at which inseparable adhesion occurs can of course be determined in the same manner by continuing the testing at higher temperatures until a point is reached at which the coating applied to the test piece byspraying is not removable therefrom intact by thermo or mechanical means. In the.

ent adhesion for certain given metal bases and The foregoing examples are intended merely as illustrations since in each case the temperature of incipient adhesion should be determined by test for the specific conditions under which the process is applied unless this temperature has been indicated by previous experience with similar materials.

One application of the discovery resides'in making molds for the manufacture of smooth moldabie articles, such as articles of rubber, plaster and formaldehyde resins and permanent molds for use in casting metals. In this case I take in the first instance a metal master or pattern having substantially the dimensions of the article to be reproduced from which any number of molds may be obtained by the application of my process, 1. e., by spraying metal against said master or pattern'to f'ormfa'poherent detachable coating of metal and thereafter detaching and removing the coating so formed. The mold so obtained is an exact negative of said master or pattern and its surface will bear the same degree of smoothness and as the original.

The method may, of course, be applied to the manufacture of a finished article of manufacture since in this case starting with a metal mold of the article the article itself may be built up by spraying metal against the surface of the mold to form a structure of the desired thickness. The finished article may be formed in this'manner or, alternatively, by first forming a shell having the external shape of the finished article and there-- after completing the article by pouring a backing of metal or other suitable material into the shell.

Articles of manufacture so produced may have a surface of one metal and a backing of a diiferent metal. Such articles may, for example, be, made having a surface of a relatively inert metal or one taking a high polish, such as brass, chromium, or stainless steel.

Mandrils or chucks for spinning may be formed by my method. These may conveniently be formed starting with the duplicate of the article 'to be spun and building against this by spraying a shape of spray metal substantially in the form of the desired chuck or mandril and thereafter detaching the same.

When making molds, articles of manufacture, etc., whenever the form from which the mold or article is made has reverse drafts, it will of course be understood that the mold or article of manuvenient or practicable the sprayed metal may be appliedupon a shape of metal, the melting point of which islower than that of the sprayed metal and the shape thereafter removed from the applied metal by melting it away.

The process is applicable to the production of negatives of metal surfaces of all kinds includingmetal surfaces themselves formed of sprayed metal.

Another application of my process is in the printing art. Metal type can be made by the application of my process by spraying upon a metal matrix and thereafter detaching and removing the sprayed metal. If desired I may in thefirst instance assemble a block of type and form the 'matrix itself by spraying thereon,

whereupon thematrix may be used for any de-- sired number of reproductions of the type either by the application of my process or by pouring metal into the matrix. In either case both the type and the matrix can be formed of metals harder than those at present generally available for this purpose in the printing industry.

It will of course be understood that dies may be formed by the process hereinabove described for the manufacture of molds, i. e., by taking a suitable master and thereafter forming the dies by spraying against the master.

It will also be understood that after I have formed a coherent coating of sprayed metal by following the method hereinabove described I ,may proceed to apply a-backing to this coating by either spraying or pouring a metal of different composition.

The foregoing description is furnished by way of illustration and not of limitation and it is, therefore, my intention that the invention be lim-' 1 ited only by the appended claims or their equivalents wherein I have endeavored to claim broadly all inherentnovelty.

I claim-- 1. Process of making metal negatives of smooth surfaced metal objects comprising spraying such a metal object with a metal, which object is at least at the temperature of incipient adhesion for said object and said applied metal, and below the a metal object with metal, which object is substantially at the temperature of incipient adhesion for said object and said applied metal, at least until the surface is covered. with applied metal, thereby forming a coherent coating of said applied metal, adhering to said metal object and thereafter removing said coating from said object.

WILLIAM C. REID. 

